i) Field of the Invention
The present invention relates to an orientation film used to orient liquid crystal molecules into a predetermined direction.
The present invention also relates to a liquid crystal device (abbreviated as LCD hereinafter). More specifically, the present invention relates to a liquid crystal device requiring color adjustment.
The present invention further relates to a liquid crystal device and a method for producing the same. More specifically, the present invention relates to a liquid crystal device wherein the direction of the optical axis of a substrate with a film optically anisotropic to the orientation axis of a displaying liquid crystal device can be adjusted in an easier and more accurate manner. The present invention furthermore relates to a method for producing a film with the above-mentioned orientation function without contaminating the surface of the film.
ii) Description of the Related Art
Prior art orientation films for liquid crystal devices include a film comprising an insulating material such as polyimide resin treated with rubbing process in a single direction using cloth and the like, a film formed by oblique evaporation of silicon dioxide (SiO.sub.2), and the like.
As to the orientation films obtained by rubbing process, however, there have been problems such as the occurrence of dust and the generation of static electricity during the rubbing process for the preparation of such orientation films.
The films obtained by oblique evaporation are too costly for the preparation thereof and the process is difficult to use for the preparation of film having a large surface area. Disadvantageously, they cannot meet the large-scale production demands of liquid crystal devices.
Prior art orientation films are also formed by stamp method.
The orientation films formed by stamp method are films produced by stamping thermoplastic-resin films formed on a heated substrate to prepare an irregular form on the surface thereof. The surface form of orientation films produced by conventional stamp method is composed of a great number of convex streaks 6 formed almost parallel on substrate 5, as is shown in FIG. 6, which is designed so that the cross section of the convex streaks 6 may be in bilateral symmetry to the vertical line pulled down from the top L thereof.
Alternatively, a conventional super-twisted nematic (abbreviated as STN hereinafter)-type LCD is in the structure shown in FIG. 21.
On substrate 41 of the LCD is formed transparent electrode 46 comprising a film of indium and tin oxide (abbreviated as ITO hereinafter). On the transparent electrode 46 is formed a film of high-molecular compounds including silicon dioxide, polyimide, and the like, after the treatment with rubbing process. In the space between two substrates 41 where orientation film 45 is formed, is arranged a displaying liquid crystal layer 42. On one of the two substrates 41, is arranged a phase-difference plate 43, on which is positioned a polarization plate 44. The phase-difference plate 43 is to be arranged for the objective to eliminate the coloring in yellow or yellowish green when the LCD is observed frontally.
Furthermore, FIG. 36 is a schematic cross-sectional view of conventional liquid crystal. The liquid crystal comprises a sandwich structure composed of a combination of two substrates 61 wherein there are formed transparent electrode 62 and the orientation film 63 formed thereon, and the two substrates 61 are adhered together with sealing agent 64. The two substrates 61 are fixed together by a given distance via the sealing agent 64. Film 66 with optical anisotropy (abbreviated as optical film hereinafter) is appropriately adhered to the substrates 61 in cell 83 prepared in such manner. The optical film 66 includes a film having a function of phase-difference plate.
The fabrication of such liquid crystal device has conventionally been carried out by the following procedures. As is shown in FIG. 36, transparent electrode 62 is formed from a film of indium and tin oxide (abbreviated as ITO hereinafter). By obliquely evaporating silicon dioxide and the like or by coating a film of a polymer such as polyimide, a film is formed, followed by subjecting the film to the rubbing process comprising rubbing the film in one direction with fibers such as nylon, polyester and the like, whereby there is formed orientation film 63 with a function to arrange displaying liquid crystal 71 described hereinbelow in a predetermined direction.
The two substrates 61 are then combined together with sealing agent 64. Into the cell 83 thus prepared is injected displaying liquid crystal 71 from the injection inlet of liquid crystal. After the injection, the injection inlet of liquid crystal is sealed.
To the substrate 61 of the cell 83 thus prepared is adhered optical film 66 preliminarily cut out from an original plate. As the optical film 66, there may be used those produced by unilaterally drawing polyvinyl alcohol and the like. At the adhesion of the optical film 66 in such manner, a relative angle between the orientation axis of the displaying liquid crystal and the optical axis of the optical film 66 should be adjusted as designed.
However, the pretilt angle of such conventional orientation film gets as small as 0 to 1 degree, with the tendency to readily cause disclination, which is a critical defect as liquid crystal.
It is generally known that disclination tends to hardly occur if the pretilt angle is one degree or more.
If orientation film is formed with the rubbing process, there occur such problems as easier generation of dust or static electricity in the orientation film and the like. There is also a problem in that the form of the surface of the orientation film formed by rubbing process is less reproducible.
On the other hand, oblique evaporation has problems in its high cost and less reproducibility.
On conventional STN-type LCD, there should be arranged phase-difference plate 43 on one of the substrates 41, which lowers working efficiency. If the phase-difference plate 43 is only slightly made to bend in the conventional LCD, the difference in index of refraction between normal light and abnormal light varies at that portion, inducing the variation in the difference in index of refraction in one phase-difference plate 43. The conventional LCD has therefore a problem in that the displaying quality of the LCD is deteriorated due to the phase-difference plate 43.
In the large-scale production thereof, furthermore, the direction of the optical axis of optical film 66 cannot be accurately adjusted to the orientation axis of displaying liquid crystal 71, which affects disadvantageously the displaying quality.
At the preparation of the conventional liquid crystal, the orientation axis is determined by the rubbing process in a predetermined direction, on the basis of the end face of the substrate 61. Alternatively, the direction of the optical axis 66 of optical film is determined by adhering the optical film 66 cut out from the original plate to the substrate 61, based on the end face of the substrate 61, so that the optical axis might be in a predetermined direction in combination with glass substrate 61.
Therefore, the axial variation when the optical film 66 is cut from the original plate as well as the positional variation when the optical film 66 is adhered to the glass substrate 61 are accumulated together, so the direction of the optical axis of the optical film has hardly been adjusted accurately to the orientation axis.
According to the method for producing such conventional liquid crystal device, the orientation film 63 is formed by rubbing process, which is the cause of the low yield due to the contamination of the surface of the orientation film 63 via the generation of dust and static electricity during the rubbing process.